I have read many how-tos on this subject and they all fell down somewhere and many other users have reported problems; so I am basically repeating existing instructions but adding notes on how to solve some common problems.1. The Jessie non-free repositories contain NVidia driver V. 340.46 which only suits modern graphics cards. By "Legacy" I am referring to earlier versions available from the Wheezy repositiories.2. Open /etc/apt/sources.lst in a text editor as sudo. You will need sudo password to do this. EG In a terminal run sudo gedit /etc/apt/sources.lst (replace "gedit" with your favourite editor}.3. Add this line: deb http://http.debian.net/debian/ wheezy-backports main contrib non-free4. Save the file5. In a terminal run: sudo apt-get update6. In many instructions you will be asked to run: "sudo apt-get -s install nvidia-glx nvidia-kernel-dkms nvidia-xconfig nvidia-settings" but this will try to get the latest version and throw errors such as "The following packages have unmet dependencies:....".7. Instead in a terminal run: sudo apt-get install nvidia-detect. Repeat this for "nvidia-support" and "nvidia-xconfig"8. Now run: sudo nvidia-detect. You will get output similar to: "It is recommended to install the nvidia-legacy-304xx-driver". You now know which driver to install. Currently the Wheezy repository has V304 and V319.9. I now find it easier to use Synaptic. In the search box enter nvidia and select to search in name only. Now check the item selected under 8 above to be installed and it will also automatically include any depencies.10. You will get a warning that a reboot is necessary before the drivers are functional. DO NOT REBOOT yet. Just keep clicking "Next" until the installation is complete.11. IMPORTANT. In a terminal run: sudo nvidia-xconfig. If you reboot without doing this you will boot to a terminal screen with a blinking cursor.12. Now reboot and NVidia will handle your graphics. You can prove this by running Nvidia X Server Settings in the Administration menu.

I hope this assists you. I found the Nouveau drivers supplied with Jessie just weren't up to the job but now I am flying!